1. Field of the Invention
This invention relates generally to absorbent fibrous structures, and more particularly to articles, such as disposable diapers, including the fibrous structures as absorbent structures thereof. In disposable diapers, the fibrous structure is employed as an internal component that preferentially directs body liquids through its thickness and away from the facing sheet.
2. Description of the Prior Art
Disposable diapers having an absorbent component disposed between a facing sheet and a backing sheet have become popular in recent years because of their relatively low cost which permits them to be economically disposed of after a single use. In designing such diapers, it is extremely important to effectively utilize the absorbent capacity of the diaper to retain discharged body liquids such as urine, and to prevent such liquids from leaking from the internal absorbent components through the facing sheet contacting the wearer (wetback). If the absorbent capacity of the diaper is not effectively utilized, or is inadequate, premature leakage of body liquids can occur. If the diaper is not properly designed to inhibit the wetback of body liquids the surface of the diaper touching the wearer's skin may become excessively wet; causing chafing and/or rash formation.
U.S. Pat. No. 3,768,480, issued to Mesek et al, is directed to a disposable diaper having a facing sheet designed for the purpose of promoting the penetration of urine through the facing sheet and into an internal absorbent batt. The promotion of urine through the facing sheet is achieved by providing a gradually increasing wettability gradient within the facing sheet. The wettability gradient is formed by intermingling one type of absorbent fibers with another type of fibers that are less wettable, and establishing an increasing concentration gradient through the thickness of the sheet for the more wettable fibers. The facing sheet is a blend of long fibers having a length greater than about 6.35 mm and short fibers having a length less than about 6.35 mm, with the short fibers being more wettable than the long fibers. The concentration of short fibers gradually increases from the surface of the facing sheet adjacent the wearer to the surface adjacent the absorbent batt. The facing sheet can be formed in accordance with the method and apparatus disclosed in U.S. Pat. No. 3,768,118, issued to Ruffo et al. The concentration gradient of short fibers imparts an increasing wettability gradient to the facing sheet, and this wettability gradient promotes the flow of urine through the facing sheet and toward the internal absorbent batt. The loosely compacted absorbent batt is constructed to be more wettable than the facing sheet to aid in drawing urine from the facing sheet into the batt. Further, after it has been initially formed, the structure of the absorbent batt is modified to encourage the effective utilization of the absorbent area of the batt to prevent localized flooding therein and undesirable wetback therefrom. As a result of the abovedescribed construction, urine is preferentially directed through the facing sheet and into the absorbent batt.
The absorbent batt disclosed in the '480 patent is modified, after its formation, by providing a paper-like densified wicking layer on one surface thereof in accordance with the processes described in U.S. Pat. No. 3,017,304 and in the '480 patent to Mesek et al. Specifically, the wicking layer is formed in situ by applying moisture to one surface of the batt, and thereafter applying pressure to the batt to densify the moistened surface. The wicking layer provides a modified capillary structure in selected regions of the absorbent batt for the purpose of promoting the desired distribution of urine.
Although the posttreating of an absorbent batt for the purpose of providing a wicking layer therein may improve the fluid distributing properties of said batt, it is believed to be desirable to initially form the absorbent batt with a capillary structure that promotes effective utilization of its absorbent capacity and aids in preventing wetback.